Introduction to the Autonomic Nervous System

Question 1

What is the exception to the “sympathetic = norepinephrine, parasympathetic = acetylcholine” rule?

Answer 1

Sweat glands of the skin are innervated by sympathetic fibers which release acetylcholine

Question 2

Activation of which system (sympathetic or parasympathetic) leads to widespread and long-lasting effects?

Answer 2

Sympathetic

Question 3

Where are the cell bodies of preganglionic neurons? Postganglionic neurons?

Answer 3

Preganglionic: In the brainstem or spinal cord
Postganglionic: outside of the CNS; collection of nerve bodies is a ganglion.

Question 4

Describe the myelination of pre and post ganglionic fibers and the neurotransmitters they release in both sympathetic and parasympathetic systems.

Answer 4

Preganglionic fibers of both systems are myelinated and release acetylcholine at terminals
Postganglionic fibers of both systems are unmyelinated and release either norepipneprhine or acetylcholine

Question 5

Where in the spinal cord are the cell bodies of the sympathetic preganglionic neurons? Which spinal cord segments are these bodies located within?

Answer 5

In the lateral gray horn of the spinal cord; from T1 to L2/L3

Question 6

Which roots of the spinal cord do preganglionic fibers travel out of, and where do they travel to?

Answer 6

They travel out of the ventral horn, enter the ventral ramus of a spinal nerve

Question 7

What is the white communicating ramus?

Answer 7

A bundle of myelinated preganglionic fibers exiting the ventral ramus to enter the sympathetic trunk

Question 8

What is the ganglion at the tip of the coccyx?

Answer 8

Ganglion impar

Question 9

On a single trunk, how many:
Cervical ganglia?
Thoracic ganglia?
Lumbar ganglia?
Sacrococcygeal ganglia?

Answer 9

Cervical: 3 (superior, middle, inferior)
Thoracic: 11 or 12
Lumbar: 4 or 5
Sacrococcygeal: 5 or fewer

Question 10

What is the fusing of the inferior cervical ganglion and the first thoracic ganglion?

Answer 10

The stellate ganglion

Question 11

What are the 4 paths that a preganglionic fiber originating in the thoracolumbar portions of the spinal cord can take?

Answer 11

1. Synapse in corresponding ganglia at that level. Postganglionic fibers rejoin spinal nerve via gray communicating ramus
2. Ascend or descend the trunk and synapse at a different level. This is the source of preganglionic fibers for ganglia above T1 or below T2.
3. Pass through sympathetic trunk without synapsing and travel via thoracic, lumbar, and sacral splanchnic nerves to collateral ganglia.
4. Pass through all ganglia (paravertebral and prevertebral) and synapse with chromaffin cells of the adrenal medulla

Question 12

How do preganglionic sympathetic fibers that innervate the head, neck, body wall, limbs, and thoracic cavity course through?

Answer 12

Either synapse in corresponding ganglia at that level or ascend/descend the trunk and synapse at a different level

Question 13

How do preganglionic sympathetic fibers that innervate viscera in abdominopelvic cavity course through?

Answer 13

Either synapse via thoracic, lumbar, and sacral splanchnic nerves to collateral ganglia or pass through all ganglia and syanpse with chromaffin cells of adrenal medulla

Question 14

What type of cells are chromaffin cells on the suprarenal gland?

Answer 14

They are modified postganglionic sympathetic neurons, and receive innervation directly from preganglionic fibers

Question 15

Where do postganglionic fibers destined for distribution within the neck, body wall, and limbs enter? Via what?

Answer 15

They enter the 31 sets of spinal nerves fro the sympathetic trunk to adjacent ventral and dorsal rami via gray communicating ramus

Question 16

What 3 functions do postsympathetic fibers stimulate after passing through the spinal nerve?

Answer 16

1. Contract blood vessels
2. Contract arrector pili muscles
3. Cause sweat glands to secrete

Question 17

Where do postganglionic sympathetic fibers to cause contraction of blood vessles, contraction of arrector pili muscles and sweat in the head synapse in (which ganglia)?

Answer 17

The superior cervical ganglion

Question 18

What is another name for the outflow of the parasympathetic outflow based on where it occurs?

Answer 18

This is also known as craniosacral outflow, because the preganglionic sympathetic fibers originate in the brainstem or at the S2-S4 sacral fibers

Question 19

Where are the cell bodies of parasympathetic postganglionic cells located?

Answer 19

In minute ganglia close to or within the organ it innervates

Question 20

What is the exception to the “no parasympathetic innervation of the limbs or body wall” rule?

Answer 20

Erectile tissue receives parasympathetic innervation

Question 21

What are the 4 parasympathetic ganglia that have specific names in the head region?

Answer 21

1. Ciliary ganglion - in orbital cavity
2. Pterygopalatine ganglion - pterygopalatine fossa
3. Otic ganglion - infratemporal fossa
4. Submandibular ganglion - floor of mouth

Question 22

What four cranial nerves carry myelinated preganglionic fibers of the parasympathetic system?

Answer 22

1. Oculomotor nerve
2. Facial nerve
3. Glossopharyngeal nerve
4. Vagus nerve

Question 23

Which cranial nerves carry parasympathetic fibers to which ganglia? (4 cranial nerves, 4 parasympathetic ganglia)

Answer 23

1. Oculomotor nerve -> ciliary ganglion
2. Facial nerve -> pterygopalatine and submandibular ganglion
3. Glossopharyngeal nerve -> otic ganglion
4. Vagus nerve: Provides most parasympathetic (75% of parasympathetic fibers) to thoracic viscera and foregut/midgut derivatives

Question 24

What is the name of the parasympathetic fibers leaving the S2-S4 region (the sacral component of the craniosacral output)?

Answer 24

Pelvic splanchnic nerves

Question 25

What organs are supplied by the parasympathetic innervation of the pelvic splanchnic nerves?

Answer 25

Hindgut derivatives (descending colon, sigmoid colon, rectum) and all pelvic organs